1. Field of the Invention
The present disclosure relates to semiconductor devices, and more particularly, to a method and apparatus for performing failure analysis of semiconductor devices with fluorescence inks.
2. The Related Art
Determining a point of failure in wafer level chip scale packages (WL-CSP's), or in product assembled to organic media, can be difficult. The point of failure may be due to either cracks in solder bumps, delamination of various organic films such as polyimide, bi-cycle butane (BCB), stress compensation layers (SCL) or soldermasks. Current cross sectioning techniques do no allow sufficient contrast to determine such a point of failure.
As known in the art, fluorescence microscopy is performed at narrow emission and excitation wavelengths, usually confined to medical and biological applications. Other reported work is in the field of metallography in the determination of metal porosity. In the preceding case, the technique lacks sufficient contrast to determine a point of failure in a wafer level chip scale package.
Fluorescent microscope technology requires costly specialized filter sets, for example, on the order of greater than $1,500.00 per set. Fluorescent microscope technology also requires high intensity light sources, for example, on the order of greater than 250 W. Furthermore, fluorescent microscope technology used in failure analysis suffers from loss of contrast between a failed area and a remaining section of the device under inspection. In addition, light from a 250 W source, for example, impinging upon a filter cube may only provide on the order of 5-6W at the output of the filter cube, under bright field illumination.
A typical failure analysis of a wafer level chip scale package includes pull testing. Such a process of pull testing can include, for example, a red dye pull test according to the following steps. To begin, the part under test is soaked in a mixture of organic solvent and red dye. The part under test is then removed from the mixture and allowed to dry. Subsequently, the part is subjected to either a shear or pull test, and tested to failure. After the shear or pull test, the process includes inspecting the part under bright light to verify if red dye has soaked into any failure point. Failure points can include one of a i.) solder crack, or ii.) delamination of epoxy to a die. However, contrast of the part under bright light is diminished, tending to render detail of the device under examination and the failure analysis less than optimal.
Another form of typical failure analysis includes bomb testing of hermetically sealed metal parts, such as TO-3 devices. The process of bomb testing includes, for example, a red dye bomb test according to the following steps. A capped part under test is placed into a pressurized vessel containing a red dye in an organic solvent. The vessel is pressurized to 100 psi and allowed to remain for 10-30 minutes. The pressure is then released and the part washed in acetone, for example, on the order of three times. Lastly, the part under test is decapped and inspected under bright field in search for dye that has ingressed into the device. However, contrast of the part under bright light is diminished, likewise rendering detail of the device under examination and the failure analysis less than optimal.
Accordingly, it would be desirable to provide an improved failure analysis that overcomes these and other problems in the art.